Movements of the OceansChapter 21

Ocean CurrentsOcean water moves in giant streams called CURRENTS.

Two categories: Surface & Deep Currents

Surface CurrentsCreated as Wind (moving air) pushes the

water causing the water to move in the same direction as the air

Made to curve due to the Coriolis Effect - the tendency of a moving object to follow a curved path rather than a straight path because of the Earth’s rotation.Northern Hemisphere – currents curve to the

right, or clockwiseSouthern Hemisphere – currents curve to the

left, or counterclockwiseCreates GYRES – huge circles of moving water

Global Ocean Surface Currents→Warm water currents → Cold water currents

Deep CurrentsCold, dense currents far below the surfaceCreated as cold, dense water of the polar

regions sinks and flows beneath warmer ocean water.Density is affected by temperature

Cold water molecules contract creating denser water that sinks

Warm water molecules are farther apart and less dense causing them to rise above more dense water

Density is affected by salinity Water with more dissolved solids is more dense and

sinks

Arctic Bottom Water is -2˚C and has high salinity making it very dense

Antarctic Deep Current

Ocean WavesPeriodic up-and-down movement of water

created as moving air pushes the water. Crest – highest part Trough – lowest partWave height – vertical

distance between crest and troughWavelength – distance

from crest to crestWave period – time

required for 2 consecutivewaves to pass a given point

Energy is transferred from water molecule to water molecule in the direction of the wave.

Water molecules move in a circular motionAt a depth of about ½ the wavelength there is

almost no circular motion of water molecules.Wave size is determined by 3 factors

1. Speed of the wind2. Length of time the wind blows3. Fetch – the distance the wind blows across

open water

Height of the wave changes as the wave approaches the coast forming breakers

Breaking waves erode sediment from the ocean floor and move sediments along the coastline

Refraction – waves bend as they approach the coastline

Longshore current – flow parallel to the shore and carry large quantities of sand

Undertow – irregular current, occurring only near shorelines, created as water carried onto a beach is pulled back into deeper water by gravity.

Rip current – a fast moving current that flows perpendicular to the shore that forms when large

breakers return to the ocean through channels that cut through underwater sandbars running parallel to the beach.

TidesPeriodic rise and fall in ocean levels caused by

the gravitational pulls of the moon and sun.Occurs every 24hours and 50min.High tide – when water level is highest in an

areaLow tide – when water level is lowest in an

areaTidal range – difference between high and low

tides

Spring TidesSun Earth and Moon are in line

(new moon and full moon)Sun and Moon’s gravitational pull

work together to increase the pull of the water and increases the tidal range

Produces higher high tides and lower low tides

Neap TidesSun Earth and Moon are at 90˚

angle (first-quarter and third-quarter moon)

Sun and Moon’s gravitation pull work against each other to reduce the pull of the water

Produces lower high tides and higher low tides.